Subject: Re: bug#61307: 30.0.50; pixel-scroll-precision-mode: window-scroll-functions?

From: Michael Heerdegen <[email-masked]>
Date: Thu, 16 Feb 2023 05:57:18 +0100

Eli Zaretskii <[email-masked]> writes:

> > > Each time you do the smallest possible scroll, by how many pixels, or
> > > by what fraction of the screen-line's height does Emacs scroll the
> > > window?  IOW, by how many pixels is the display scrolled for each call
> > > to window-scroll-functions?

> I hoped you will answer the specific questions I asked, quoted above.
> But since you don't have a device to actually observe
> pixel-scroll-precision-mode on your system, something I didn't know
> until now, I guess you cannot answer them?  (I also don't have access
> to a suitable system, otherwise I wouldn't have bothered you with the
> questions.)

[ I'm sorry, I totally misunderstood your question as rhetorical, for me
to think and understand ]

I'm using a normal wheel mouse.  I have nevertheless enabled
`pixel-scroll-precision-mode' for two reasons: I want to have the
animated "smooth scrolling" like known from browsers, which looks nicer
and seems to be better for the eyes/ the brain.  And I want to get a
better scrolling experience for images (pdf, and such things).

And the answer to your question is: I get a scroll amount of
approximately 7 lines per <wheel-up> or <wheel-down> event.  I
configured pixel-scroll-precision-interpolation-factor to 1.5, the
original value of 2.0 was a bit too large in my experience.

> > But I understand that what I see when scrolling with a normal wheel
> > mouse is only one case we need to handle.

> Right.  Though on such a system, we should probably call
> window-scroll-functions every scroll.

Is receiving <wheel-up> and <wheel-down> events a sufficient hint that
the user is scrolling using a "normal" wheel mouse?

Michael.